i've implemented the firebug-replacement.
you can use Debug.isTest() in javascript to limit console.log()-calls to non-live environments (has the same restrictions as Director::isLive(), just regexing the url for ".test" and ".dev"). you can override this behaviour with Debug.set_environment_type(). see http://doc.silverstripe.com/doku.php?id=debug

then again, console.log()-code should not be committed at all - it produces a javascript-error if the firebug-replacement is not existing.